Purification of liquids



Oct. 17, 1944. E M KELLY Ei-AL PURIFICATION OF LIQUIDS Filed Sept. 18,1941 Patented Oct. 17, 1944 rUamcA'rroN or LlQUms Earl M. Kelly andArthur M. Kivari, Los Angeles, Calif., assignors to The Dorr- Company,Inc., New York, N. Y., a-corporation of Delaware Application September18, 1941, Serial No. 411,269

- 2 claims. (ci. 21o-2) This invention relates to..purifl cationtreatment of impure waste liquids having particles in suspension thereinand having septical organic matter that requires to have its biochemicaloxygen demand lessened, if not satisfied. Such wastes are illustrated bysewage, and wastes from packing houses, canneries, dairies, oilrefineries and.

the like.

Purification of liquids in its broadest sense includes two types oi'treatment. One by which suspended solids or other particles areseparated from their 'carrying liquid, which is .herein calledclarification, and the other by Awhich the oxygen demand of the liquidissatisfied, which is herein.

called purification, that word being thus used station from which-isdelivered to the combination filter-bed and clarifier a clear efiiuenteven though high in B. O. D., the combinationfilterbed and clarifier cando a' much better ,10b in that it needs only to dobiologic purificationwork;

Thus the use of a vacuum notation clarification apparatus ahead of acombination trickling filter and clarifier, has a cumulative effect o nthe latin a rather limited or specific sense. A major object of thisinvention is to carry out both clarication and purification efficientlyin apparatus that is highly effective, reasonably cheap to install andequally cheap to operate dependably.

Waste liquids heretofore have been usuallyy sub-- jected to treatmentinmechanically cleaned clarifier orv apparatus in which suspendedI solidsare settled into the form of sludge in machines that operate as a resultof sedimentation. Such machines are-.effective in so far4 as settleablesolids are concerned but where a liquid has many floatable suspendedsolids such as particlesl of turbidity, the floated solids form into ascum that a clarifier is not ordinarily equippedto handle. Accordingly,one of the features of this invention is the vuse of a machine that isdesigned not only to handle normally oatable solids but also cause tofloat certain normally non-floatable solids or suspended particles.Thus, this invention proposes to use on waste liquids a machine whichinduces the floatio of suspended particles by the ter in a variety ofways. l

In the combination filter-bed and clarifier assembly, the biologicorganisms of the filter-bed, or at least some of them. feedon theseptical organic material of the liquid which they convert, somedirectly and someindirectly, into a Stabilized purified liquid. But inthis 'process some solids are coagulated or agglomerated by the biologicorganisms thus leaving some suspended solids in the discharge from thefilter-bed. Also as the liquid filtering or percolating through thefilter- 'bed is in effect vaerated, the filter-bed discharge usually isemitted from the'filter-bed in a condition wherein it has some floatingsolids and some air. This condition is not well handled in an ordinaryclarifier, but if this liquid, after having vits normally settleablesolids sedimented therefrom, is carried back and treatedv in the vacuumflotation machine, the air and iloatable solids are removed therefrom inthat machine, which reuse of vacuum effects. By the use of such amachine,

it is found that polluted waste liquids are clarified of their pollutingseptical matter in a highly efficient manner, so that the clarifiedeffluent emitted or discharged from such va machine is substantiallyfreed or ridded of its suspended matter.

In the purification of polluted liquids or those having septicalorganics therein, this invention proposes to use the combination oftrickling filterbed in combination with a mechanically cleaned clarifierin circuit therewith. In such a combination, the biochemical oxygendemand (B. O. D.)

l can be satisfiedor lessened, effectively, b ut heretofore, such acombination has been called upon to do the work of clarification as wellas biologic purification. We have found that if the process ofclarification can be well carriedout -ln one sults in considerableadvantage. By the elimination of practically all of the suspended solidsin the liquid prior to its reaching the trickling filterclariflercombination, the latter can be made smaller and thus decrease theinstalled cost thereof as well as operation costs, Less ground space isthusl required. Less ground space is also needed for the vacuumflotation machine as compared with` the usual clarifier, and as thevacuum flotation machine is` covered, it makes a more slghtly apparatusin that the odorous scum is maintained out of sight, and obnoxious odorsare prevented from escaping into the surrounding atmosphere.

In the usual trickling filter-bed, .there is a tendency of suspendedsolids to clog the interl to starve'for want of air. By removingsubstantially all suspended matter from the liquid passing to thefilter-bed, this trouble ls assuredly avoided. With the avoidance ofthreat of pond# ing, liquid can be ,supplied to the filter-bed atgreater rates, so a bottle-neck is thus overcome -for'the capacity oi'the filter-bed in this new arrangement is not dependent upon keeping itin non-ponding condition. Its effective capacity is solely the rate atwhich it can purify liquid passed therethrough. If polluted liquid bepassed through a trickling filter-bed only, the stability of the degreeof purity of the discharged liquid is not necessarily constant. Indeed,the B. O. D. of such liquid usually reverts or increases with thepassing of time. But the purity of the emitted liquid can besubstantially stabilized or fixed if the filter-bed be v4placed in acircuit withv a clarifying tank whereby liquid being treated flows fromone to the other and back again, more or less in closed circuit and in amanner whereby new liquid can be fed to the circuit while treated liquidis released from the circuit. The time of detention in the circuit ofthe liquid being treated controls the degree of stabilizationof thereleased eiiluent. Thus this invention proposes to use such a circuitfor the purification station and preceding that station is a vacuumflotation clarificaliquid from the apparatus, and means for discouragingair leakage into the tank through said discharges. Details ofconstruction and operation of such a machine are given hereinafter.

The trickling filter-clarifier assembly for use in the practice of thisinvention is characterized in that it comprises a filter-bed of discretefilter media such as rubble or cinders to the surface of which liquid isapplied by means of rotating arms that spray therefrom liquid to betreatedl in the bed. On the media of the bed, there are maintainedactive aerobic biologic organisms ranging from bacterial ora. up throughworms and crustaceans'. Piping is arranged to a Vflowpath between thefilter-bed and a mechanically cleaned clarifier or sedimentation tank.And

piping is also arranged to provide a flow-path between the tank to theinowing feed for the filterbed. This permits a complete cyclic flowbetween filter-bed and clarifier. Feed means are provided for thecircuit and efiluent release means are also provided for the circuit.The `clarifier or sedimentation tank of this circuit can bemade smallerthan` otherwise if the liquid passing through the piping from theclarifier to the filter-bed, Vis withdrawn directly from the liquidcontents of the clarifier rather than being withdrawn from the efuentthat has left the clarifier. The reason for this is that since thedegree of stabilization of the purity of the effluent leaving theclarifier at the circuit is dependent upon the time of detention of theliquid in the circuit, by recircu-- lating liquid while it is within thecircuit before it is released therefrom, the recirculating liquidcomprises all that which is in the circuit including that which is inthe filter-bed and the clarifier. In other words, by this means therecan be a high circulating load in the circuit,

whereas if the clarifier enluent were being circulated, then theclarifier would be two or more times larger than itwould be otherwise inorder to get the same detention period.

e The beet embodiment ef this invention` new -s known is chosen for -thepurpose of illustration herein. It is shown diagrammatically orsymbolically herein with' only enough detail shown for an understandingthereof. The showing is not mechanically complete because single lineshave been used wherever possible and especially for piping and novattempt has been made to show the presence of pumps or valves since itis believed obvious to use them wherever needed.

` The embodiment illustrated is not to be taken as limited because theinvention is capable of being practiced with modified forms of apparatuswithin scope of the appended claims.

Therefore, in the accompanying drawing only one figure has been shownwhich illustrates diagrammatically one embodiment of this inventionsince this invention relates 'to the combination of a type of vacuumflotation-machine in cooperative arrangement and which acts conjontlywith the circuit which includes a filter-bed and a clarifier to producenew technical effects. The vacuum fiotation apparatus will be describedfirst and thereafter the lter-bed clarifier combination will bedescribed.

The vacuum flotation apparatus suitable for practicing this invention lsmore completely described in a co-pending patent application of Packardand Clemens, filed September 17, 1941, Serial No. 411,110. However, itis believed that suflicient understanding of the type lof vacuumflotation apparatus suitable for use in practicing this invention can begleaned from the following description: A

Reference numerals have been used. They have been applied to illustrateparts asfollows:

The letter V is used to indicate generally the yvacuum flotationapparatus which comprises a gas-tight closed tank II' to whichgas-containing liquid I2 is fed to the tank through an opening I3 in thebottom I4 thereof and passes upwardly 'through a draft tube I5upstanding in the tank that terminates in a flared portion I6 having amouth I1 from whichffeed liquid is emitted into the tank in a regionadjacent the liquid level I8 therein. The liquid level oi the encasedbody of liquid I9 in the tank is maintained or controlled in theembodiment shown by means of an overflow weir 20 suitably supported inthev tank by means such as brackets 2|. Liquid overflowing the weir 20passes into a launder 22 from which it flows or is removed from the tankby means of clarified eflluent discharge pipe 23. 24 represents a baillepreferably annular that extends into the liquid body I9 to a region 25thereof in which there is a minimum of suspended solids. Above' theliquid level Il in the tank is a sas-receiving and collecting space 26.21 represents a suction of vacuum pump capable of producing on the lliquid in the tank the effect of vacuum. 28 indiscum arms l2, rotatedfrom shaft II that is moytivated by motor driven gears u. The shaft 33may also vrotate the draft tube It'with sludge sludge discharge pipe 38each has associated withv it a barometric leg arrangement marked "B toprevent substantial air leakage through it into the tank Il. 'I'he drafttube I5 thus emits or releases influent feed liquid adjacent the liquidlevel I8 of that part of the liquid that is surrounded by the baffle 24.Floatingscum is removed from the same region in that the ro tating arms32 sweep scum floating on the liquid encircled by the baille 24 to andinto the hopper 29 for discharge. However, clarified eiiluent leaves theliquid body i9 by overflow Weir 20 into launder 22 `in a region that isfunctionally leased from the mouth Il of the flared portion I6 of thedraft tube lfbecause the clarified' effluent is drawn from the liquidbody i9 in effect from a region indicated by the lower edge 25 of thebaille 26. The weir 20 thus controls the liquid level i8 in the tanksince the baffle 24 divides the liquid body of the tank in the twobalancing columns of which one between the baille 2t and the Weir is acolumn C of clariiled liquid which balances the other column C that isencircled by the bafe 2d and comprises liquid beingclarifled, plusfloating scum. The column within the baille 2d is somewhat taller thanthe column o f clarified liquid because it includes floating scum.

Scum passing lfrein the barometric leg on scum discharge pipe 3@ andsediment discharging from the barometric leg on sludge discharge pipe 30can join and be passed to further treatment of disposal. from thebarometric leg ont-he eiiiuent pipe 2d is conveyed through pipe d@ to acircuit indicated generally by D that comprises a trickling Y filter-bedli made up of filter material or media of discrete particles such asstone or binders. In such a bed it is usual to supply feed liquidthereto through a hollow column l2 from whence the Vliquid. isdistributed over the surface of the bed by being emitted throughrotating radial armsv 43. The arms are rotated usually by the reactionof liquid leaving the trailing side of the arms through nozzle-likeorifices. Liquid that percolates through the stone in the bed illcomprises lter-bed discharge and is passed through pipe Qd to asedimentation tank d5 having an overflow discharge sa. The tank may beequipped with a cleaning mechanism for lmpelling sediment or sludge todischarge through pipe d8. 'I'his discharge sediment may also join thesediment or sludge from scum outlet pipe Sii and sludge outlet pipe d8of the vacuum apparatus V. The pipe @d thusprovides a.'iownath forfilter-bed discharge passing from the filter bed Il to the clarier 4E.Another flow-path is provided in pipe t9 through which liquid may nassto the filter-bed feed pipe dil to be mixed with feed incoming to thefilter-bed whereby the filter-bed is thus continually supplied with amixture of new feed and liquid recirculated from the clarifier 45. Thepipe 89 preferably is arranged to conduct to the filter-bed di liouidthat is taken directly from the liquid contents of the clarifier 45 forreasons given herein elsewhere.

Liquid fed for. treatment in the vacuum flotation apparatus V should begas-containing. Under some conditions liquid to be treated has sum-Claried effluent C passing' cient gas to produce the flotation effectsdesired under the influence of vacuum, but usually it does not. In sucha case the liquid must have gas diffused therein in a gassing station.Such a station is indicatd by tank or basin 50 to which impure liquid issupplied through pipe 5i. The basin is 'provided with a baille 52 forpreventing short-circuiting of the feed liquid. In the basin -50 meansare provided for diffusing gas in the liquid. Such means can be animpeller agitator for pumping gas or air into the liquid quickly andviolently as shown, for instance, in the patent application of Kelly etal., Serial No. 399,058 and filed June 21, 1941.' This type is to berecommended where a high degree of solids .removal is desired. However,it may be desired when treating sewage and the like, to substitute forthe'more efficient short violent gassing of the liquid, a gentle andprolonged gas-diffusing action by means of placing in the basin 5Uporous tiles vor plates 53 to which is pumped through pipes or manifolds54 compressed air or gas compressor 55. The compressed air is carbonatedin tiny bubbles which become entrained in the impure liquid in a highlysatisfactory manner. Some of the bubbles grow to be large, so it isimportant that they be removed from the liquid, and this can be done bypassing the gassed liquid to a de-gassing or de-aerated chamber or zoneassociated with the basin E@ which is in eilect a zone of relativequiescenceof gas and some scum 59 which inevitably cclv lect hereoverflow the baffle bl' back into the main bodyy of the basinb wherethey are diffused into the liquid. The gas or fouivapors that escapefrom the tank are collected in a gas space 58 beneath the top 59 of thebasin from'whence theylilow to gas dome il@ and through pipe 6I todischarge or for further treatment. Gassed and de-gassed liquid thenilow from the basin 5d through pipe i? to the vacuum flotation machineV. Air may be used for the gas-diffusing action on some liquids but whentreating sewage and other liquids having a relatively high biologicoxygen demand, air is used to satisfy this demand rather than to aerate.So when such liquids are to be gassed, it is preferable to gas them withthe gas that is relatively inert to the oxygen demand and such gassesare illustrated by carbon dioxide and nitrogen or a combination thereofAthat may include some air. Since this invention has as one of itsobjects the satisfying B. O. D. of the liquid treated the satisfying ofthat B. O. D. to some degree in a crasslng station relieves to thatextent the load of B. O. D. satisfaction that would otherwise fall on n.trickling filter circuit D.

Some liquids such as sewage have suspended particles. especiallyparticles of turbidity. namely. those that are colloidal that aredifllcult of sedimentation unless flocculated. Flocculation of theseparticles can be facilitated if chemicals are added to the sewage suchas at 82 prior to their entry into the gassing basin bil. Thesechemicals such as alum or ferric chloride tend to removed from theirliquid in the vacuum apparatus V and therein are eliminated prior totheir reaching the filter circuit D. Since the gashandled by asubsequent sewage apparatusI therefor. 63 indicates a station where thiscomminuting takes place. 64 indicates the incoming raw sewage or otherwaste liquid to be treated. The sediment discharging from the clarifier45 through the pipe 48 may Well have in it certain gas or vacuumfioatable solids, so optionally some at least of that sediment may beconducted through pipe 65 back to be mingled with the liquid flowing tothe vacuum apparatus V for treatment therein and preferably back to theconduit 5I in advance of point such as 62 Where chemicals possibly arebeing added. l

The operation of this clarification and purification system is asfollows: gas-containing impure liquidthat is to be treated to removetherefrom suspended partclesfand to satisfy or reduce the biochemicaloxygen demand of the liquid with possibly to stabilize the reducedbiochemical oxygen demand against reversion, is supplied to the vacuumflotation apparatus V through draft-tube I5 up which the liquid :Bowsdue to the effect of vacuum produced in the tank I I by means of suctionor vacuum pump 21. LThe feed is emitted or released into the body ofliquid I9 already in the tank', substantially adjacent to theliquidlevel I8 which by means of 'overflow Weir means 20 is controlled ormain# tained, since the height of this Weir establishes the generalliquid level of the liquid in the tank II. As soon as the liquid isemitted from the flaring upper terminal I1 of the draft-tube I5 (if notsomewhatlsooner) the effect of Vacuum in the tank operates to float andto accumulate as scum not only those suspended particles of the feedthat are normally floatable but many that are not normally floatable.The floating scum, or iioat, is swept along the liquid level by therotating scum sweeping or impelling arms l 32 until it encounters theramp 3I up which the scum is impelled 'to and into the scum hopper 29from whence it flows down pipe 30, through the barometric leg B on thatpipe, 'to discharge or for further treatment. It is tov be notedthat-the scum is thus removed approximately from its place of formationand also in the'region of the feed release, a region that is encircledby the substantially annular bafile 24. This baille extends `into theliquid body I9 in the tank to a point of termination that is in theregion where there is a minimum of suspended solids in the liquid sinceits lower termination comprises the region from which clariged eflluentis in effect drawn from the tank II through the column C oi' clarifiedliquid that overflows weir 2l) into launder 22 from whence it is removedfrom the tank through eilluent pipe 23 and its barometric leg B. Thepoint of termination of this baille 24 is determined somewhat by thedegree of vacuum on the tank. Vacuum equivalent of from seven to nineinches of mercury has been found to operate satisfactorily, so the pump21 is operated accordingly.v At that rate, the eiiluent should be takenoff from the liquid body I in the tank at a submerged point vat whichthe effect of vacuum corresponds approximately to about only flve inchcsof mercury. The dimensions of a satisfactory tank have been found tohave a liquid depth of about I0 feet and three inches in which case the'baffle 24 should terminate at 25 about ve feet from the tank bottom I4.Another function of the baiile 24 is to serve as a dividing meansbetween column C of clarified liquid and column C' of liquid beingtreated plus its floating scum. These are columns that balanceeachother. The eilluent take-off over the Weir 20 is thus from a regionthat-is functionally remote from the place where the incoming feedliquid is emitted into the tank. It is also functionally remote fromlthe place of discharge of the floating scum. Thus by-passing isprevented. In such a vacuum flotation apparatus about 40% of thesuspended solids in the feed liquid is removed from the tank as scum.Certain solids in the feed liquid are not floatable even under theeffect of vacuum, so they settle onto the floor I4 of the tank wherethey form into sediment or sludge 'from whence they are impelled byrotating sludge impelling blades 38 on arms 35 into sludgesump 31 fromwhence in turn the sludge can be discharged through pipe 38 through itsbarometric leg B to discharge or 4liti to further treatment. 'I'hedetention time required for liquid in the vacuum flotation tank V isfrom three to seven minutes, and clarified liquid can be discharged fromthe tank at rates ranging from 5,000 to 101,000 gallons per 24I hoursper square foot of liquid level surface in the tank. The rate overfioweddepends upon the degree of clarification required of the eiiiuent. Forinstance, in treating cannery wastes, itmay be desirable to goappreciably below `5,000 gallons,'so'

this and the upper quantity of 10,000 gallons are not our extremelimits.

The vacuum apparatus removes from 40-80% -and upwards of the suspendedsolids of the liquid treated thereby, so eilluent emitted from thevacuum flotation apparatus V is substantially ridded of suspendedsolids. However', it still may have a relatively high biochemical oxygendemand. Such effluent is then passed through pipe 40 to a circuit D inwhich the biochemical oxygen demand is satisfied or at least lessened.The vacuum flotation treated eilluent passes through pipe 40 to beapplied and distributed over the surface of the filter-bed 4I fromwhence it percolates through the discrete material of the bed meanwhilebeing subjected to the action of aerobic biologic organisms whose majorfunction in this bed is to reduce the biochemical oxygen demand of theliquid transmitting the bed in a downward direction. Liquid that hasthus been subjected to biologic action passes from the filter-bed asdischarge and is flowed through pipe 44 to a clariiler or sedimentationtank 45.` Herein the liquid is detained in quiescent sedimentation sothat suspended solids therein can settle to the floor of the clarifierin the form of sludge or sediment. Such sediment is impelled todischarge by sludge impelling rakes 41 and passes through pipe 48 tofurther treatment.

'I'he biologic organisms in the filter-bed 4I have at least two effects,of which one is to satisfy or reduce the oxygen demand of liquid thatthey encounter and the other is to coagulate or agglomerate suspendedsolids. In any ordinary or usual trickling filter-bed both of thesefunctions are made use of but it has been found that substantiallyinproportion as they are not required to coagulate suspended solids,their eiilciency in reducing oxygen demand is increased. Therefore, y

it is a teaching ofthis invention to relieve them as much as possible oftheir solids coagulating acting by' doing that for them in the treatmentof the impure liquid before it reaches the filterbed. namely doing it inthe vacuum flotation apparatus V. But however much the solidscoagulating is done for them in advance, there are always somel solidsthat they succeed in coagulating, and it is these unavoidably coagulatedsolids that are to lbe caught and sedimented in the clarifier v46.However, the clarifier 4B has a further and much molle importantfunction, namely as a supplemental place where active biologic organismsare maintained and wherein they do oxygen -satisfying work. The-organisms incubate readilyl and grow in the filter-bed but due to themore or less rapid flow ofliquid through the bed, such organisms arewashed or swept therefrom into the clarifier where they live, work, andthrive. They thrive because the filter-bed has an aerating effect on theliquid passing therethrough so thatv it contains a substantial quantityof dissolved oxygen, which ls..an environment conducive to continuedactivity. of the organisms. Therefore, if the liquid normally iiowing tothe filter-bed is augmented in volume with liquid continuallyrecirculated through pipe 49 to a point aheadof the filter-bed from theclarlfier, the filter-bed is dosed with liquid at a rate suiiicientlyhigh to wash living organisms into the clarifier and sufficiently highto carry with the lliquid entrained oxygen into the clarifier.

Athe preferred one.

and the clarifier in the circuit D, so the clarifier could 'come firstand receive clarified eilluent from the vacuum machine V, with thefilter-bed comingnext in the circuit, instead ofthe sequenc'e shown.However, the sequence shown is In the embodiment shown, liquid, prior toits introduction into the vacuum apparatus V is subjected to an aeratingor gassing operation followed by a de-aerating or degassing operation.This is carried out in the station illustrated by basin 50 wherein airor gas is bubbled through the liquid to bring about ashigh anentrainment as possible in the liquid of minute bubbles. The smaller thebetter. In-

deed, bubbles of microscopic size are best or most effective in aidingin the subsequent vacuum flotation of the suspended solids or otherfloatable particles. This can be done preferably by passing gascompressed in compressor 55 through porous tiles or plates 53 in thebasin bottom for these tiles tend toemit bubbles of very small size.

Thus, by this arrangement, the filter-bed can b e I made smaller thanusual because some of its oxygen satisfying capability is transferred tothe clarifier. Thus in the circuit vD made up of a filter-bed and aclarifier, there is a high circulating liquid load, in which as well asin the filterbed and clarifier, oxygen satisfaction is continuallytaking place.

The circuit has another function, ynamely of stabilizing the degree ofoxygen satisfaction of the eilluent therefrom, for triclling filter-bedeffluent may be reasonably purified when released,

but it has the `unhappy facultyy of being nonstable in that its oxygendemand will increase again progressively within a few days. to overcomevthis tendency and thus make ythe oxygen satisfaction more or lesspermanent and thus stabilized, it has been found that this stabilizationisa function ofthe time of detention of the liquid within the circuit D.The time of detention should be of the order of two hours, although thetime depends uponthe degree' of stability required.n For total stability(for 15 days or more) with substantially no oxygen demand, a total oflsix hours detention should be given, but as sanitary engineering.requirements are usually less than that, the degree obtained isproportionate to the proportion of six hours detention that is made useof. If liquid to be recirculated to the filter-bed for augmenting itsfeed,

, were drawn fromy the clarifier effluent, the 4clariof the .bacteriamade use of is only twenty minutes: the faster they are recirculated,the more effective is the use that can be made of their life In orderThereafter the gassedA liquid passing into the degassingcompartment 56Where bubbles larger than the small ones' are permitted to break or torise along with scum at 58 from whence they overflow weir 51 back intobasin 50 where they arebroken up and dispersed due to theagitationtherein. The liquid passing to the vacuum apparatus V should have enoughair or gas therein, so to that end it has been found that gas shouldfbesuppliedv thereto at the rate oi' from 0.02 'to 0.05 cubic feet pergallon of liquid based upon average iiow, depending upon the flotationconditionsl to be encountered, and in order to be sure that this amountof gas is entrained inthe.

liquid, the liquid should be detained in the gassing station or basin 50for aperiod of from 5 to 20 minutes depending upon the rate at which gasis being supplied thereto.

When it is desired to occulate suspended sol- I ids in the gassing zone50', coagulating chemicals can be supplied to and mixed with the liquidin some chemical feeding station as at 62 whereupon they produce theircoagulating effect which is emphasized as flocculation under theinfluence of the gentle agitation in the basin 50. These fiocsA arefragile and should not be broken up. so that if fiocculation is to bemade use of gentle agitation in the basin 50 should be used, in whichcase the aeration or gassing by the use of porous tilesis recommended,and thelonger detention period should be used. But if for any reasonAfiocculation is not needed, and no chemicals are to be used, amechanical impeller aerator can be substituted for the moregentle andprolonged aerating by means of the porous tiles or plates. In thisevent, no compressor 55 is needed. However. the use of chemicalsandiiocculation is to be recommended because this aids in the removal inthe vacuum apparatus V of fine solids and especially colloids whichotherwise would pass from the vacuum apparatus in its clarifiedeffluent, and their presence would place a burden of coagulation on thebiologic organisms in the the feed of mipure iilter-bed circuit D thatit is one object of this invention to discourage. Solids in the influentwaste liquid that are larger than can be conveniently handled by theapparatus of this invention are treated in station 63 either (1) toremove them completely as by screening, or (2) by comminuting them intoa size that can be handled. Foul vapors accumulated from the liquid inthe gassing station 50 can be conducted through gas dome Bil and rpipe6l to a' place of disposal, to which pipe 60 can be Joined pipe 28 thatconveys exhaust gases, and further foul vapors from the vacuum pump 21.Some of the technical effects attained by the use of this invention are:when treating wastes and particularly cannery wastes, in a tricklingfilter-bed-hereoiore by usual methods, floating particles or materialhave not been eliminated from the liquid passing for treatment in thefilter-bed, and this material has tended to clog the bed to itsdetriment. This has been a proby lem that to date has not been solved,but it is solved nicely by the vacuum flotation treatment ahead of thefilter-bed. The biologic organisms are relieved of their usual solidscoagulating dutyA and thus it has been found that they can function moreeiiiciently by being left solely to satisfy oxygen demand. And by.assuranceof absence of clogging, the capacity of the filter-bed can beincreased, or its size decreased which is the same thing. The solidscoagulating function of the, organisms for colloidal material is noteven necessary, in the practice rof this invention, for that material iscoagulated and occulated in the gassing station so that it issubstantiallyremoved in the vacuum apparatus. Floatable and colloidalmaterial in the sludge discharged from the clarifier that is in theillterbed circuit that has heretofore been a problem,

can be disposed of by retreating that material in the vacuum flotationapparatus. A trickling lter-ibedhas been heretoforeodoriferous, whereasby the practice of this invention the foul odors or vapors aresubstantially eliminated from the waste liquid before it reaches thelter-bed circuit. Less ground space i's required by the vacuum flotationapparatus than any known pretreatment apparatus for trickling filters,and the filter-bed circuit of this invention also requires less groundspace because it can be made abnormally small. Scum is substantiallyeliminated from the surface of the clarifier in the filter-bed circuit,and scum in the vacuum apparatus is maintained out of sight in that the'vacuum tank is enclosed. The entire apparatus isvsuitable forcontinuous operation. and is substantially foolproof, so that highlyskilled operators are not needed. Less total metal is required-in such aplant, which is an important item in the defense program. especiallywhen so many sewage treatment plants are being required camps andstations. v v

We claim: 1. The process for the treatment of waste liquids havingoxygen-demanding liquid and susconstituents including those particles ofturbidity inhibitory to -aerobic bacterial action, which comprisessubstantially ridding such liquid taining [an encased ever-changing bodyof such liquid suspension having an overlying gas-holding space,controlling the liquid level of such body, maintaining the liquid levelof the body at sub-atmospheric pressure by applying suc'- tion equal tomore than 6 inches of mercury to gas of said gas-holding space andthereby to said level, continually projecting gas-bearing impure feedliquid and its suspended constituents to adjacent the liquid level ofthe body and into the reach of the suction used which is sumcient thatsuch constituents are both buoyed and sucked to as well as held at theliquid level collecting as scum, continually removing from a region inthe body functionally remote from the scum a clarified oxygen-demandingliquid from which such scum constituents have been substantially soremoved, continually removing scum from the body; and thereaftercontinually passing emuent freed of a signiilcant quantity of itsturbidity to purication treatment in a biologic trickling filter-bedcircuit wherein there is maintained a mass of active aerobic bacterialorganisms and a bedy'of liquid undergoing sedimentation, sub-'1 saidgas-holding space and thereby to the liquid vlevel to maintain on saidlevel sub-atmospheric pressure. means for continually projectinggasbearing-impurefeed liquid having oxygen-demanding liquid andsuspended constituents including particles oi' Aturbidity inhibitory toaerobic bacterial action to adjacent such liquid level and into thereach of the suction used which is sufficient that such constituents aresucked to as well as both buoyed and held at'the vliquid level asfloating, scum, means for vcontinually re-l moving from a region in thebody shielded from the-scum a clarined oxygen-demanding liquid fromwhich such scum constituents have been substantially so removed, meansfor removing such scu-n from the body; and in combination with theforegoing a purifying section including circuit-providing meanscomprising an aerobicV biologic trickling filter-bed,l la sedimentationtank, piping providing aflowpath for filter-bed discharge to thesedimentation tank, and piping providingv a now path for liquid derivedfrom the sedimentation tank to the filter bed, means for supplying suchsuction-treated clarified ogygendemanding liquid rid of a significantquantity of its inhibitory constituents to said circuit derived fromaregion in said tank functionally remote from said scum, and means forremoving from said-circuit the end products.

EARL M. KELLY.

ARTHUR M. maar. 1

